1. Field of the Invention
The invention relates to a mobile crane with a telescopic jib.
2. Discussion of the Prior Art
In order to increase the roller height, it is known for a lattice mast extension to be rigidly bolted on the head of the main jib of a mobile crane (in this regard, see extracts from the brochure Mannesmann Demag Fordertechnik, Demag AC 1600, pages 5, 17; Apr. 24, 1996). In order to enlarge the operating range of loads of equal weight which are to be hoisted, it is chosen to use a rockable auxiliary jib (see Demag AC 1600, pages 23, 24, 27, 28). A disadvantage here is that the auxiliary jib must additionally be transported and mounted on and dismounted from the main jib.
German reference DE 39 34 783 A1 discloses a crane which has an outrigger which, for its part, comprises a plurality of sections interconnected by joints. This crane is intended to be used as a multipurpose crane employed as a crane not only to hoist objects such as, for example, steel girders, but, at the same time, to support construction work. The essential elements of this crane are a basic frame, a drive part for driving and controlling the crane, which can be rotated on the basic frame in a horizontal plane, an articulated arm, attached to the drive part, which can be folded together and extended in a vertical plane, and a gripping device for gripping structural elements. The gripping device is connected to the front end of the arm in a fashion capable of tilting and being removed. A disadvantage of this design is that the jib length cannot be varied continuously in a direct fashion, but only by appropriately angling the individual links of the arm. Moreover, this design is not suitable for road transportation, since the articulated arm has to be partially dismounted. The articulation of the arm also limits the supported load which can be hoisted.
A generically determinative crane is disclosed in German reference DE 29 50 884 A1. This crane has a telescopic jib which comprises a base unit and a plurality of telescoping segments which can be extended and retracted by means of a telescopic device. The telescoping segments are connected to the base unit so that they can be pivoted in the direction of the jib. Arranged in the head region of the base unit is an angle insert whose inclination can be continuously adjusted via a piston-cylinder unit. The piston-cylinder unit is arranged on the underside of the jib, specifically such that the cylinder is pivoted at the underside of the base unit, and the piston rod is fastened to a comer point of the angle insert. The second corner point of the angle insert is connected to the telescoping segment situated after the bending point, while the hinge of the angle insert is arranged on the head of the base unit.
It is a disadvantage of this arrangement that it is thereby possible to bridge only very low troublesome edge heights, since this is essentially determined by the length of the base unit.
A slightly different design is shown by German reference DE B 19 65 118. In this known telescopic jib, there is arranged in the innermost telescoping segment a displaceable extension piece which, in its fully extended longitudinal position can be pivoted about the connecting element out of the position aligned with the longitudinal direction of the innermost telescoping segment, and can be fixed with respect thereto in predetermined pivot positions by means of a latch. The latch forms a stop in the aligned position of the extension piece. For the purpose of arranging the extension piece, a cutout is provided in the head part of the innermost telescoping segment and a plurality of recesses arranged on a circular arc around the connecting element are provided in the foot part of the extension piece. The latch engages in these recesses in the pivoted position of the extension piece.
The need to cut through the head part of the innermost telescoping segment is disadvantageous in this arrangement, with the result that the roller head configuration and the cable guidance are rendered difficult. A further disadvantage is that the longitudinal extent of the extension piece is limited, and the angling away can be done only in discrete angular degrees.